The present invention relates to a rotation angle sensor having a variable reluctance resolver (hereinafter referred to as a VR resolver) for an axis combination angle 1X (single combination angle) and a VR resolver for an axis combination angle nX (n combination angle) wherein, n is 2 or an integer greater than 2.
Conventionally, resolvers, and other angle measuring devices, for which the axis combination angle is 1X, have primarily been used as a location detector. The axis combination angle is the ratio of the output electrical angle relative to the input mechanical angle of the detector. For example, when n multiplied by mechanical angle θ1=electrical angle θ2, the axis combination angle is indicated as nX (n combination angle).
First, the structure of a conventional resolver is described. FIGS. 5A and 5B show a representative conventional resolver.
The stator windings 101 in FIG. 5A are formed consecutively via crossing hooks 103 arranged on the stator yokes 102. The ends of the stator windings 101 are connected together and coupled to the connector portion 104. The shapes of the salient poles of the rotors 105 are formed in a way such that changes of the gap permeance in the direction of the circumference are appropriate. Accordingly, the amplitude of the output signal of the stator windings 101 corresponds to a sine wave with seven cycles per rotation depending on the position of the rotors 105. In this example, there are seven salient poles on the rotors 105.
Japanese Unexamined Patent Application Publication 2001-183169 discloses that such a position detector has the following problems.
A resolver with an axis combination angle 1X allows simultaneous detection of the angle, the magnetic pole and the original point by resolver/digital (R/D) converting a two-phase signal that is changed to a sine wave. The sine wave has a 90-degree phase shift per single cycle for each rotation of the axis. However, to obtain high resolution, the resolution of the R/D converter has to be increased, which is costly. Although the absolute position can be detected, the precision of detection depends on the electrical precision of the resolver. In other words, at all rotation angles, the manufacturing error and the temperature error directly affect the electrical precision. In addition, to improve the precision of the detection, the precision of the analog signal has to be increased. However, due to the effect of the winding precision included in the signal, the detection of the angle position at a high precision is difficult. Consequently, a position detector is more expensive and difficult to employ compared to a general resolver.
Furthermore, when the axis combination angle is increased, for example, when the axis combination is set to be 100×, 100 times precision can be obtained. If the signal precision is the same, however, implementation applications are limited to, for example, multiple motors, where the number of rotors is one hundred.
At the same time, when the application is focused on a multi-use motor with a low number of poles, position detection with high precision can be obtained. What has been proposed is a combination of a position detector with a small axis combination angle and a position detector with a large axis combination angle.
FIG. 6A shows a conventional multi-speed resolver system. FIG. 6B is illustrates the relationship of the output signals of the double resolver. FIG. 6C is an explanatory drawing that describes a method to find the rotation angle for the multiple-speed resolver system of FIG. 6A.
As shown in FIG. 6A, a multi-speed resolver system includes a resolver 110 and a digital converter 114. Depending on the application, an analog converter can be employed instead of the digital converter 114. In the resolver 110, the output of resolver 112 with an axis combination angle nX that is directly connected to the rotation shaft 111 becomes an axis combination angle nX resolver signal. The output of resolver 113 with axis combination angle 1X, which is connected to rotation shaft 111 with a mechanical device such as a gear system, is an axis combination angle 1X resolver signal.
The digital converter 114 carries out the following process. The axis combination angle nX resolver signal is converted to the sawtooth wave at the bottom of FIG. 6C by the R/D converter 115 in advance. The axis combination angle 1X resolver signal is converted to one of the triangular waves at the top of FIG. 6C via the R/D converter 116. Then both of the signals are recorded by the synthesizing circuit 117. Next, both resolver signals at the measuring point are input, and, based on the axis combination angle 1X resolver signal Ak, angle θk is found from the triangular wave at the top of FIG. 6C. The rotation angle Bak corresponds to the axis combination angle nX resolver signal Bk measured from the peak of the sawtooth wave (single triangular wave) of the axis combination angle nX resolver signal corresponding to angle θk.
FIG. 6B is an exemplary illustration of each of the resolver signals and indicates the sinusoidal resolver outputs. FIG. 6B indicates the relationship between the sine signal wave of the axis combination angle 1X resolver and the sine signal of the axis combination angle nX resolver (when n=2).
When two resolvers are employed as in FIG. 6A, the required space increases and the generation of a mechanical processing error is inevitable. In addition, a gear connection is arranged at the joint of the shaft, so the axial length of the shaft increases.
Therefore, instead of using two resolvers with the same axis combination angle, position detection at a high precision is carried out by combining a position detector with a small axis combination angle and a position detector with a large axis combination angle. However, the position detector uses magnetism and light, and therefore in general, it is difficult to obtain a sine wave signal with a long cycle. In addition, the manufacturing of a small axis combination angle is simple for a differential-mode transformer-type resolver. However, when a resolver with a large axis combination is manufactured, the number of winding poles increases, and consequently, manufacturing is complicated and the size increases.
To obtain a high detection resolution by eliminating the problems in the prior art position detector discussed above, a multi-speed resolver with multiple poles is disclosed in the same Japanese publication (Japanese Unexamined Patent Application Publication 2001-183169), as shown in FIG. 7. FIG. 7 shows a conventional multi-speed resolver with multiple poles.
In the example of FIG. 7, two resolvers are arranged in parallel on the rotation shaft. A first resolver 122 has a rotor iron core 121 with an axis combination angle 50X, which has 50 rotor teeth. A second resolver 124 has a rotor iron core 123 with an axis combination angle 49X and has 49 rotor teeth. A value L is found by subtracting detected position value K of the 49th cycle of the second resolver 124 from the detected position value J of the 50th cycle of the first resolver 122. Then, the value N, which is L times M, is obtained from the following judgment conditions. In other words, the detected position value N of the axis combination angle 1X, is found.
N=L×M wherein, when L≧0, E=0; and when L<0, E=360°.
In the Japanese publication mentioned above, forty-nine and fifty teeth have to be provided respectively on the rotors, accurately and in alignment. The multi-speed resolver requires a processing circuit to produce the output signal of the axis combination angle 1X by finding the difference of the axis combination angle based on the number of teeth. Numerous teeth have to be formed on the stator in correspondence with the teeth of the rotor, and consequently, the manufacturing is difficult.